1. Field of the Invention
This invention relates to the field of pencil plotters and, in particular, to a lead positioner for a pencil plotter in which a shaker mechanism enables leads to be individually released from a lead stocker into a lead holder.
2. Description of the Related Art
The use of pencil plotters has increased significantly in the making of graphics and drawings due to the ability of designers and draftsmen to be able to make alterations or corrections to such graphics and drawings. In order to increase the flexibility of the pencil plotters, it is desirable that lead holders carrying different hardnesses or colors of lead be able to be easily placed into and removed from the pencil carriage. In addition, it is necessary to have a mechanism for being able to replace the lead in a lead holder by a lead of the same hardness or color when the lead has been used up. The latter problem has been generally solved by having a plurality of removable lead holder carousels, each one holding a plurality of lead holders of the same kind. When the lead in a lead holder is used up, the lead holder in the pencil carriage is replaced by a lead holder in the carousel. When a lead of different hardness or color is desired, the lead holder is transferred from the pencil carriage to the carousel and the carousel is replaced with a carousel carrying lead holders having the desired hardness or color. More recently, plotter designs have been introduced having a single carousel carrying a plurality of lead holders of differing hardnesses and colors and having the positions of the lead holders indexed so that the pencil carriage can receive a lead holder carrying a lead of desirable hardness of color. The problem still remained, however, of replacing a lead when it had been used up without having to replace the entire carousel with a new carousel in which the leads have been renewed.
In order to solve such lead replacement problem, the use of lead stockers has been employed. Such lead stockers are similar to lead holder carousels in that they are rotatable and carry a plurality of chambers or magazines into which a plurality of replacement leads of differing hardnesses and colors can be inserted. In theory, the rotatable lead stocker can be indexed to the rotatable lead holder carousel and a lead of proper hardness or color can be transferred into the corresponding lead holder when its lead has run out. In practice, however, problems have arisen in the mechanization of the transfer process, particularly in assuring that a single lead from the plurality of replacement leads will, in fact, be ready to be transferred from the lead stocker chamber into the lead holder and that the lead stocker is properly positioned with respect to the lead holder when the lead is to be transferred from the lead stocker to the lead holder. While various jolting or bumping techniques have been tried to free a single lead and various motorized positioning techniques have been employed to ensure a proper positioning of the lead holder and lead stocker before lead transfer, these techniques have been found lacking in consistency and reliability.
Thus, it is a primary object of the present invention to provide an improved lead positioner for a pencil plotter.
It is another object of the present invention to provide an improved lead positioner for a pencil plotter which assures a reliable transfer of lead from a lead stocker to a lead holder.
It is a further object of the present invention to provide an improved lead positioner which enables a single lead from a plurality of leads in a lead stocker chamber to be consistently transferred to a lead holder.
It is still another object of the present invention to provide an improved lead positioner which assures that a lead stocker is properly positioned with respect to a lead holder when a lead is to be transferred from the lead stocker to the lead holder.